Reversible screen for electrophotographic printing

ABSTRACT

An apparatus in which an original document is housed to form a continuous tone light image thereof. The apparatus is arranged to illuminate the original document and to create a finely divided uniformly distributed light image. A selectable feature therein permits the formation of sharply focused light images or softer, de-focused light images.

United States Patent [1 1 McVeigh 1 Oct. 21, 1975 REVERSIBLE SCREEN FOR ELECT ROPHOTOGRAPHIC PRINTING Inventor: James H. McVeigh, Rochester, NY.

Assignee: Xerox Corporation, Stamford,

Conn.

Filed: June 3, 1974 Appl. No.: 475,731

US. Cl 355/3 R; 96/45; 355/75 Int. Cl. 603G 15/00 Field of Search 355/3 R, 75, 76, l33, 17,

References Cited UNITED STATES PATENTS 2/[964 Carlson et al 96/45 X 3,152,528 lO/l964 Pendry ..96/45X Primary Examiner-Richard L. Moses Attorney, Agent, or Firm-H. Fleischer; J. J. Ralabate; C. A. Green [57] ABSTRACT An apparatus in which an original document is housed to form a continuous tone light image thereof. The apparatus is arranged to illuminate the original document and to create a finely divided uniformly distributed light image. A selectable feature therein permits the formation of sharply focused light images or softer, de-focused light images.

20 Claims, 4 Drawing Figures US. Patent Oct. 21, 1975 Sheet 1 of2 3,914,040

U.S. Patent Oct. 21, 1975 Sheet2 0f2 3,914,040

O O O O O O O O O O O O O O O o o o o o o o o o o c o c o o o o o o o o o o o I o o o o o o o 0 Q) I FIG 3 FIG. 2

REVERSIBLE SCREEN FOR ELECTROPI-IOTOGRAPHIC PRINTING BACKGROUND OF THE INVENTION This invention generally relates to an electrophotographic priming machine, and more particularly concerns an apparatus for housing an original document therein so as to produce continuous tone light images therefrom.

A typical electrophotographic printing machine is provided with a transparent platen upon which an original document is supported. An optical light image of the original document is created and recorded as an electrostatic latent image upon a charged photoconductive surface. The electrostatic latent image is then developed with charged particles to produce a powder image thereof. Thereafter, the powder image is transferred to a sheet of support material and permanently affixed thereto forming a copy of the original document.

Conventional screening methods may be employed in an electrophotographic printing machine. Such methods produce the effect of tone graduation plus variations in dot size. In the highlights, the dots will be small and will increase in size through the intermediate shades until they merge together in the shadow region. At the extremes there will be complete whiteness at the highlight end of the tone scale and nearly solid black at the shadow end. This type of tone structure can be reproduced in an electrophotographic printing machine.

An example of this is found in U.S. Pat. No. 2,598,732 issued to Walkup in 1952. This patent discloses a plate disposed on top of a photoconductive insulating layer which is positioned face down on top of an exposure box containing a lamp. The exposure box has a glass top panel which is covered with a fine sheet of cellophane having a screen pattern applied to its un dersurface. The lamps are initially actuated so as to expose the photoconductive surface to the screen image which consists of alternate black and transparent areas. This results in a corresponding electrostatic pattern on the photoconductive insulating layer. If the plate has been previously exposed to a continuous tone image, it is now ready for the development. Contrawise, if screen exposure is made first, the plate is ready for continuous exposure.

With the advent of multi-color electrophotographic printing, wherein a plurality of differently colored toner particles are deposited in registration with one another onto the copy sheet, it became desirable to produce soft or sharp copies as well as continuous tone copies. The foregoing may also be achieved by the utilization of a screen. The thickness of the screen may be employed to either focus or de-focus the light image so as to create the desired effect in the copy.

Accordingly, it is primary object of the present invention to improve the screen employed in electrophotographic printing machines to produce soft or sharp continuous tone copies.

SUMMARY OF THE INVENTION Briefly stated, and in accordance with the present invention, there is provided an apparatus for housing an original document therein.

In the preferred embodiment thereof, the apparatus includes a support member, a plate member, and illuminating means. The support member is arranged to hold the original document with the plate member interposed therebetween. One surface of the plate member has a substantially opaque screen portion. This screen portion is adjacent to the transparent portion of the plate member. Means are provided for illuminating the original document to create a light image thereof. The light image is transmitted through the plate member forming a continuous tone light image.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects and advantages of the present invention will become apparent upon reading the following detailed description and upon reference to the drawings in which:

FIG. I is a schematic perspective view of an electrophotographic printing machine incorporating the features of the present invention therein;

FIG. 2 is an elevational view, partially in section, depicting the screen and platen for supporting the original document in the FIG. I printing machine;

FIG. 3 is an elevational view of one embodiment of the FIG. 2 screen; and

FIG. 4 is an elevational view of another embodiment of the FIG. 2 screen.

While the present invention will be described in connection with a preferred embodiment, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION For a general understanding of the disclosed electrophotographic printing machine, in which the present invention may be incorporated, reference is had to the drawings wherein like reference numerals have been used throughout to designate like elements. FIG. 1 schematically illustrates an electrophotographic printing machine arranged to create multi-color reproductions from an original document. The original document may either be a transparent, opaque, or translucent item in the form of single sheets, books, or three dimensional objects.

As illustrated in FIG. 1, the electrophotographic printing machine includes a photoconductive member having a rotatable drum 10 with a photoconductive surface 12 secured thereto and entrained thereabout. Drum 10 is mounted on a shaft (not shown) and adapted to rotate in the direction of arrow 14. This moves photoconductive surface 12 sequentially through a series of processing stations. A timing disc is mounted at one end of the shaft of drum 10, thereby activating the appropriate processing stations for producing the desired sequence of events in the printing machine. U.S. Pat. No. 3,655,377 issued to Sechak in 1972 describes a suitable type of material which may be employed as a photoconductive surface.

For the purposes of the present disclosure, the various processing stations in the path of movement of photoconductive surface 12 will be briefly described hereinafter.

As drum 10 rotates in the direction of arrow 14, it passes through charging station A. Charging station A has positioned thereat a corona generating device, indicated generally at 16, which charges photoconductive surface 12 to a relatively high, substantially uniform potential. Corona generating device 16 extends in a generally transverse direction across photoconductive surface 12. This readily permits corona generating de vice 16 to produce a spray of ions for charging photoconductive surface 12. Preferably, corona generating device 16 is of the type described in US. Pat. No. 2,778,946 issued to Mayo in 1957.

After photoconductive surface 12 is charged, drum l rotates to exposure station B. At exposure station B, photoconductive surface 12 is exposed to a color filtered light image of the original document. A moving lens system, generally designated by the reference numeral l8, and a color filter mechanism, shown generally at 20, are located in exposure station B. US. Pat. No. 3,062,108 issued to Mayo in l952, describes a moving lens system suitable for electrophotographic printing. Similarly, US. Pat. No. 3,775,006 issued to Hartman et al. in 1973, teaches the use ofa color filter mechanism suitable for the electrophotographic printing machine depicted in FIG. 1. With continued reference to FIG. 1, original document 22 is disposed upon a plate member, indicated by the reference numeral 24, which is interposed between support member 26 and original document 22. Plate member 24 has a screen on one surface thereof with a partially light scattering interface. In one mode of operation, when a sharply focused light image of the original document is desired, the screen is placed adjacent to original document 22. In another mode of operation, when a softer, slightly de-focused light image is desired, the screen is placed adjacent to support member 26. Support member 26 includes a substantilly transparent member so that the light rays transmitted from original document 22 may pass therethrough. A suitable mechanism may be con nected to plate member 24 to automatically rotate it from a first position, wherein the screen contacts the original document, to a second position, wherein the screen contacts the support member. This rotating mechanism is designated by the reference numeral 28 and may include a rod 29 attached to plate member 24. When rotator 28 is actuated, it translates plate member 24 to remove it from support member 26. After plate member 24 is removed from support member 26, rod 29 is rotated so as to move the screen from the first position to the second position. Continuing now with the description of exposure station B, as shown in FIG. 1, original document 22 is supported upon plate member 24. Support member 26, which contains a transparent viewing platen, is disposed therebeneath. Plate member 24 and support member 26 will be described hereinafter in greater detail with reference to FIGS. 2 through 4, inclusive. Lamp assembly 30 is disposed beneath support member 26, and in conjunction with lens system l8 and filter 20, moves in a timed relationship with drum to scan successive incremental areas of original document 22. In this manner, a flowing light image of original document 22 is created and arranged to irradiate the charged photoconductive surface 12. During exposure, filter mechanism interposes selected color filters into the optical light path. Successive color filters operate on the light rays passing through lens 18 to create a single color light image which records a single color electrostatic latent image on photoconductive surface 12. The foregoing single color latent image corresponds to a pre-selected spectral region of the electromagnetic wave spectrum.

After the electrostatic latent image is recorded on photoconductive surface 12, drum 10 rotates to development station C. Three developer units, generally indicated by the reference numerals 32, 34 and 36 are positioned at developmemt station C. A suitable development station employing a plurality of developer units (in this case three) is disclosed in co-pending application Ser. No. 255,259 filed in l972. The development units disclosed therein are magnetic brush development units. A typical magnetic brush development unit employs a magnetizable developer mix having carrier granules and toner particles. The magnetic brush forms a directional flux field continually to create a brush of developer mix. This developer mix brush is brought into contact with the electrostatic latent image recorded on photoconductive surface 12. The toner particles adhering electrostatically to the carrier granules to the developer mix are attracted by the greater electrostatic force to the latent image and render it visible. Development units 32, 34 and 36, respectively, contain discretely colored toner particles. Each of the toner particles contained in the respective developer unit corresponds to the complement of the single color light image transmitted through filter 20. For example, an electrostatic latent image formed from a green filtered light image is rendered visible by depositing green absorbing magenta toner particles thereon. Similarly, electrostatic latent images formed from blue and red light images are developed with yellow and cyan toner particles, respectively. It should be noted, however, that during any one cycle, only one toner powder image is developed and transferred to support material 38. Hence, it is apparent that three cycles are required in order to completely transfer each of the respective toner powder images to sheet 38. After the electrostatic latent image recorded on photoconductive surface 12 is developed, drum 10 rotates to transfer station D. At transfer station D, the toner powder image adhering electrostatically to photoconductive surface 12 is transferred to sheet 38. A bias transfer roll, shown generally at 40, recirculates sheet 38 and is electrically biased to a potential of sufficient magnitude and polarity to electrostatically attract toner particles from photoconductive surface 12 thereto. A suitable electrically biased transfer roll is described in US. Pat. No. 3,612,677 issued to Langdon et al. in 1971. Transfer roll 40, preferably, is of the same diameter as drum l0 and rotates at substantially the same angular velocity therewith. Thus, as transfer roll 40 rotates in synchronism with photoconductive surface 12, successive toner powder images may be transferred to sheet 38. As depicted in FIG. 1, transfer roll 40 rotates in the direction of arrow 42.

Turning now to the sheet feeding path, sheet 38 is advanced from a stack 44 supported on a tray member 46. Feed roll 48, in operative communication with retard roll 50, separates and advances the uppermost sheet from stack 44. The advancing sheet moves into chute 52 and is directed into the nip of register roll 54. Thereafter, gripper fingers 56, mounted on transfer roll 40, secure releasably thereto support material 38 for movement in a recirculating path therewith. In this manner, successive toner powder images are attracted electrostatically to sheet 38 in superimposed registration with one another so as to form a multi-layer toner powder image thereon. After the successive toner powder images have been transferred to sheet 38, gripper fingers 56 raise support material 38 from transfer roll 40. As transfer roll 40 continues to rotate in the direction of arrow 42, gripper bar 58 is interposed between support material 38 and transfer roll 40 to separate support material 38 therefrom. Thereupon, endless belt conveyor 60 moves support material 38 to fixing station E.

At fixing station E, a fuser, indicated generally at 62, permanently affixes the transferred toner powder image to sheet 38. One type of suitable fuser is disclosed in US. Pat. No., 3,498,592 issued to Moser et al. in 1970. After the fixing process, sheet 38 is advanced by endless belt conveyors 64 and 66 to catch tray 68 for subsequent removal therefrom by the machine operator.

Following the transfer process, invariably some residual toner particles adhere to photoconductive surface 12. Cleaning station F, the final process station in the direction of rotation of drum as indicated by arrow 14, removes these residual toner particles. A pre-clean corona generating device (not shown) neutralizes the charge on photoconductive surface 12 and the residual toner particles. This enables fibrous brush 70 to remove the residual toner particless therefrom. US. Pat. No. 3,590,4l2 issued to Gerbasi in 1971 describes a suitable brush cleaning device.

It is believed that the foregoing description is sufficient for purposes of the present application to describe the features of the electophotographic printing machine in which the apparatus of the present invention is incorporated.

Referring now to PK]. 2, support member 26, preferably includes a substantially rectangular transparent member 72, made of glass, which is secured by suitable means to the frame of the electrophotographic printing machine depicted in FIG. 1. Transparent platen 72 rests upon resilient means of a solf edge gasket 74 which is secured to the horizontally dependent flange 76 of the rigid machine frame. A cover plate 78, affixed to the machine frame, is placed thereover and provided with an opening therein to expose transparent platen 72.

Plate member 24 is located on platen 72. As shown therein, transparent portion 80 is adjacent to platen 72 with screen 82 being opposed therefrom. In this mode of operation, screen 82 is in contact with original document 22. However, one skilled in the art will appreciate that plate 24 may be reversed such that screen 82 is adjacent platen 72 and transparent portion 80 is opposed therefrom. It should be noted that screen 82 is formed on a translucent layer or substrate 81 which adheres to a transparent portion or substrate 80. Transparent portion 80 may preferably be made from a suitable transparent plastic or glass material. By way of example, screen 82 may be printed on partially translucent substrate 81 by a suitable chemical etching technique, by being printed thereon, or by being photographed thereon. The screen itself may be made from any number of opaque metallic materials suitable for chemical etching, such as copper or aluminum. Translucent layer 81, preferably, is a blush coating mechanically, chemically or photographically produced.

The cover member or platen cover 84 is mounted pivotably along one edge of support member 26 and includes a substantially rigid continuous outer shell 86 having affixed thereto a resilient sheet member 88 made of an elastomeric material such as a solt rubberlike backing. Resilient sheet 88 may be fabricated from any suitable rubber such as polyurethane which is affixed to outer shell 86 by means of a suitable adhesive. Resilient sheet 86 is flexible and colored white to reflect light rays therefrom. Cover member 84 is pivotable about a suitable hinge 90 and is adapted to have the resilient portion thereof engage the original document when it is placed on plate member 24. A suitable handle 92 is provided on cover member 90 to facilitate the raising and lowering thereof.

Turning now to FlG. 3, there is shown plate member 24 with screen portion 82 having a plurality of equally spaced lines 94 thereon. Screen 82 may have anywhere from to 300 lines per inch.

FIG. 4 depicts another embodiment of plate member 24 wherein screen 82 includes a plurality of equally spaced dots 96 thereon. Once again, dots 96 are formed on a translucent or a substantially transluent material 81 and adhere to transparent portion 80. The dots may be deposited onto the translucent portion 81 by a suitable evaporative or chemical etching technique as will as by printing and photographic techniques.

One skilled in the art will realize that a variety of patterns may be used for screen 82, several examples are rows of small squares entirely surrounded by black or opaque areas, a checkerboard pattern of tranpatent and opaque areas, transparent areas continuously cover with circular black or opaque dots, or a black or opaque background covered with random distribution of transparent dots of various sizes. Any one of several screen patterns may be employed. A finer screen size generally results in a more natural or higher quality copy. Hence, while a coarse screen having 50 to 60 dots or lines to the linear inch will be useful for some purposes such as direct production of half tone images, fine screens, such as those having 100, 200, 300, 400 and even more dots or lines to the inch will give a more nearly continuous tone appearance to the finished copy. With finer screens, the screen pattern may be barely perceptible in the finished copy and the copy will have the appearance of a continuous tone photograph. The contrasting appearance obtained without the use of a screen is eliminated or greatly reduced and large black areas are rendered with apparently uniform density throughout.

The most significant parameters effecting the degree of image softness on the copy are the extent of translucency and the thickness of support 24. Softness increases as the thickness of support 24 increases and as the degree of translucency of translucent layer 81 increases.

in recapitulation, it is evident that the apparatus of the present invention produces a substantially continuous tone image approximating photographic quality. This image will, in general, be reproduced by a multicolor electrophotographic printing machine to produce a color copy approximating the characteristics of the original document in tone and quality. The foregoing is achieved by the employment of a plate member having a screen on one surface thereof. in order to create a sharply focused image, the screen is placed adjacent to the original document. Contrawise, if a soft, slightly defocused copy is desired, the screen is placed adjacent to the platen, opposed from the original document. Thus, one is able to create the type of copy most suitable for one s need and most pleasing to the eye.

[t is, therefore. apparent that there has been provided in accordance with the present invention. an apparatus for producing continuous tone copies having sharp or soft characteristics. This apparatus fully satisfies the objects. aims and advantages that are set forth above. While the present invention has been described in conjunction with specific embodiments thereof. it is evident that many alternatives, modifications and variations will be apparant to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations within the spirit and broad scope of the appended claims.

What is claimed is:

1. An apparatus for creating a light image of a document, including:

a housing;

a light source mounted on said housing;

a support member mounted on said housing for holding the document in a light receiving relationship with the light rays emitted from said light source;

a reversible plate member interposed between said support member and the document with one surface thereof being in contact with said support member and the other surface thereof being in contact with the document, said plate member comprising a first substantially transparent layer and a second layer having a screen pattern thereon; and

a lens mounted on said housing and positioned in the path of the light rays transmitted from the document through said plate member to form a light image thereof.

2. An apparatus as recited in claim 1, wherein said plate member further includes a third translucent layer interposed between and contacting the first and second layers thereof.

3. An apparatus as recited in claim 2, wherein said plate member is positioned to have the first layer in contact with said support member and the second layer in contact with the document creating a focused light image thereof.

4. An apparatus as recited in claim 2, wherein said plate member is positioned to have the second layer in contact with said support member and the first layer in contact with the document creating a de-focused light image.

5. An apparatus as recited in claim 2, further including means for moving automatically said plate member from a first position wherein the first layer contacts said support member and the second layer contacts the doc ument to a second position wherein the second layer contacts said support member and the first layer contacts the document.

6. An apparatus as recited in claim 2, wherein the screen pattern of the second layer of said plate member includes a plurality of substantially equally spaced lines.

7. An apparatus as recited in claim 2, wherein the screen pattern of the second layer of said plate member includes a plurality of substantially equally spaced dots.

8. An apparatus as recited in claim 2, further including a cover member mounted movably in said housing to secure the document on said support member in the closed position while permitting the placement of the document on said support member in the opened position.

9. An apparatus as recited in claim 8, wherein said support member includes:

a substantially rigid frame member having an aperturc therein mounted on said housing;

resilient means secured to said frame member on the periphery of the aperture therein; and

a transparent member having a generally planar surface for holding the document thereon, said transparent member being mounted on said resilient means in the aperture of said frame member permitting light rays to be transmitted therethrough.

10. An apparatus as recited in claim 9, wherein said cover member includes:

a substantially rigid outer shell having one end region thereof mounted pivotably on said housing; and

a resilient sheet member secured to the inner surface of said outer shell so as to engage the document with said cover member being in the closed position.

1!. An electrophotographic printing machine of the type having a device for charging a photoconductive surface to a substantially uniform potential and an exposure mechanism for creating a light image of an original document arranged to be recorded on the photoconductive surface, wherein the improvement includes:

a support member mounted on the printing machine,

said support member being arranged to hold the original document in a light receiving relationship with the exposure mechanism; and

a plate member interposed between said support member and the original document so that the light image thereof passes through said plate member, said plate member comprising a substantially transparent portion and a screen portion mounted on one surface of the transparent portion.

12. A printing machine as recited in claim 11, wherein said plate member includes a translucent portion interposed between the screen portion and the transparent portion of said plate member.

13. A printing machine as recited in claim 12, wherein said plate member is positioned with the screen portion thereof being adjacent the original document to form a focused light image.

14. A printing machine as recited in claim 12, wherein said plate member is positioned with the screen portion thereof being adjacent said support member to form a de-focused light image.

15. A printing machine as recited in claim 12, further including means for automatically moving said plate member from a first position wherein the screen portion of said plate member is adjacent the original document to a second position wherein the screen portion of said plate member is adjacent said support member, said moving means being adapted to return said plate member from the second position to the first position.

16. A printing machine as recited in claim 12, wherein the screen portion of said plate member includes a plurality of substantially equally spaced clots.

17. A printing machine as recited in claim 12, wherein the screen portion of said plate member includes a plurality of substantially equally spaced lines.

18. A printing machine as recited in claim 12, further including a cover member operatively associated with said support member, said cover member being movable from an opened position permitting the original document to be placed in the housing apparatus to a 9 l closed position securing the original document releassaid resilient means in the aperture of said frame ably therein. member permitting the light rays to be transmitted 19. A printing machine as recited in claim 12, therethrough. wherein said support member includes: 20. A printing machine as recited in claim 19,

a substantially rigid frame member having an aperwherein said cover member includes:

ture therein; a substantially rigid outer shell; and resilient means secured to said frame member on the a resilient sheet member secured to said outer shell periphery of the aperture therein; and and being adapted to engage the original document a transparent member having a generally planar surwhen said cover member is in the closed position.

face, said transparent member being mounted on 0 

1. An apparatus for creating a light image of a document, including: a housing; a light source mounted on said housing; a support member mounted on said housing for holding the document in a light receiving relationship with the light rays emitted from said light source; a reversible plate member interposed between said support member and the document with one surface thereof being in contact with said support member and the other surface thereof being in contact with the document, said plate member comprising a first substantially transparent layer and a second layer having a screen pattern thereon; and a lens mounted on said housing and positioned in the path of the light rays transmitted from the document through said plate member to form a light image thereof.
 2. An apparatus as recited in claim 1, wherein said plate member further includes a third translucent layer interposed between and contacting the first and second layers thereof.
 3. An apparatus as recited in claim 2, wherein said plate member is positioned to have the first layer in contact with said support member and the second layer in contact with the document creating a focused light image thereof.
 4. An apparatus as recited in claim 2, wherein said plate member is positioned to have the second layer in contact with said support member and the first layer in contact with the document creating a de-focused light image.
 5. An apparatus as recited in claim 2, further including means for moving automatically said plate member from a first position wherein the first layer contacts said support member and the second layer contacts the document to a second position wherein the second layer contacts said support member and the first layer contacts the document.
 6. An apparatus as recited in claim 2, wherein the screen pattern of the second layer of said plate member includes a plurality of substantially equally spaced linEs.
 7. An apparatus as recited in claim 2, wherein the screen pattern of the second layer of said plate member includes a plurality of substantially equally spaced dots.
 8. An apparatus as recited in claim 2, further including a cover member mounted movably in said housing to secure the document on said support member in the closed position while permitting the placement of the document on said support member in the opened position.
 9. An apparatus as recited in claim 8, wherein said support member includes: a substantially rigid frame member having an aperture therein mounted on said housing; resilient means secured to said frame member on the periphery of the aperture therein; and a transparent member having a generally planar surface for holding the document thereon, said transparent member being mounted on said resilient means in the aperture of said frame member permitting light rays to be transmitted therethrough.
 10. An apparatus as recited in claim 9, wherein said cover member includes: a substantially rigid outer shell having one end region thereof mounted pivotably on said housing; and a resilient sheet member secured to the inner surface of said outer shell so as to engage the document with said cover member being in the closed position.
 11. An electrophotographic printing machine of the type having a device for charging a photoconductive surface to a substantially uniform potential and an exposure mechanism for creating a light image of an original document arranged to be recorded on the photoconductive surface, wherein the improvement includes: a support member mounted on the printing machine, said support member being arranged to hold the original document in a light receiving relationship with the exposure mechanism; and a plate member interposed between said support member and the original document so that the light image thereof passes through said plate member, said plate member comprising a substantially transparent portion and a screen portion mounted on one surface of the transparent portion.
 12. A printing machine as recited in claim 11, wherein said plate member includes a translucent portion interposed between the screen portion and the transparent portion of said plate member.
 13. A printing machine as recited in claim 12, wherein said plate member is positioned with the screen portion thereof being adjacent the original document to form a focused light image.
 14. A printing machine as recited in claim 12, wherein said plate member is positioned with the screen portion thereof being adjacent said support member to form a de-focused light image.
 15. A printing machine as recited in claim 12, further including means for automatically moving said plate member from a first position wherein the screen portion of said plate member is adjacent the original document to a second position wherein the screen portion of said plate member is adjacent said support member, said moving means being adapted to return said plate member from the second position to the first position.
 16. A printing machine as recited in claim 12, wherein the screen portion of said plate member includes a plurality of substantially equally spaced dots.
 17. A printing machine as recited in claim 12, wherein the screen portion of said plate member includes a plurality of substantially equally spaced lines.
 18. A printing machine as recited in claim 12, further including a cover member operatively associated with said support member, said cover member being movable from an opened position permitting the original document to be placed in the housing apparatus to a closed position securing the original document releasably therein.
 19. A printing machine as recited in claim 12, wherein said support member includes: a substantially rigid frame member having an aperture therein; resilient means secured to said frame member on the periphery of the aperture therein; and a transparent member having a genErally planar surface, said transparent member being mounted on said resilient means in the aperture of said frame member permitting the light rays to be transmitted therethrough.
 20. A printing machine as recited in claim 19, wherein said cover member includes: a substantially rigid outer shell; and a resilient sheet member secured to said outer shell and being adapted to engage the original document when said cover member is in the closed position. 